A very demanding fish

The migration of salmon from the sea to the rivers is well known and is an essential part of the fish’s lifecycle – it immediately makes us think of thousands of salmon leaping en masse. Young fish migrate from the rivers into the sea, where they reach sexual maturity and then return in their thousands to reproduce. Surprisingly, they return to spawn in the sections of water where they hatched years earlier. This behavior, known as “homing,” demonstrates their high cognitive abilities, something that is not normally associated with fish. Three senses are involved in helping salmon find their home waters: they are guided by the Earth’s magnetic field and visual landmarks, but most importantly by scent. In general, all salmon species have developed a remarkably fine sense of smell, which helps them to locate prey and even escape predators. Depending on the location of their breeding grounds, the sexually mature animals migrate in late summer or fall. This is extremely challenging and pushes the fish to their limits. Seas and rivers are not only different in terms of salinity but also their currents, water depth, and turbidity. In order to get to their original spawning grounds, they will swim distances of up to 700 kilometers (435 miles). The majority of males die from the exertion afterward, but 10-40 percent of females survive and overwinter in the river or return to the sea in the fall. Some of them will return to their home waters a year or two later to spawn.